The present invention relates to an image-transfer ink ribbon provided on the same surface of a base film with an ink layer adapted for transferring an ink image on a printing medium and an image-protective layer serving for forming a protecting layer for the ink image transferred on the printing medium. In addition, the present invention also relates to an image-transferred member produced by heat-transferring an ink image and an image-protective layer on a printing medium such as a printing paper, using the image-transfer ink ribbon.
Heat-transferring systems are known as one of methods for forming an image on a printing paper based on an image information prepared by personal computers or the like. Hitherto, the images formed on the printing paper, for example, those prepared by sublimation-type heat transfer system using sublimable or thermally-diffusible dyes, have been covered by laminating an image-protective layer made of a thermoplastic resin thereover to protect the dye image.
In this case, such an image-protective layer is required to have various functions or properties such as shielding of the images from gases which causes image deterioration, ultraviolet absorbing properties for preventing discoloration or fading of the image, a resistance to plasticizers for preventing the image-forming ink from migrating into various plasticizer-containing products such as erasers, abrasion properties, a resistance to sebum or the like. Further, it is required that the image-protective layer has, in addition to these image-protecting functions or properties, an aqueous ink-printing or stamping ability in order to provide substitutes for silver salt photographs such as photographs for certificates.
As methods for laminating the image-protective layer over the afore-mentioned image, there are known a method of thermocompression-bonding the image-protective layer on a surface of the printing medium on which the image to be protected is formed, by using heat rollers, a method of adhering the image-protective layer onto the surface of the printing medium on which the image to be protected is formed, at a normal temperature by using an adhesive, or the like. Also, there is known a method of preparing a transfer-type image-protective film composed of a base film and an image-protective layer laminated thereon, and heat-transferring the image protective layer on the image to be protected to laminate the image-protective layer over the image.
In the case where such a transfer-type image-protective film is used, since only portions of the image-protective layer thereon which are heated upon the heat-transferring are laminated over the image to be protected, the printing paper on which the image is formed is prevented from being curled after lamination of the image-protective layer. Further, in the case where an image-transfer ink ribbon having an ink layer and an image-protective layer on the same surface thereof, i.e., a so-called laminating film-integrated ink ribbon, is used, the formation of the ink image and the laminating of the image-protective layer can be performed sequentially and continuously within a heat-transfer printer.
Incidentally, in general, the process for the production of the afore-mentioned laminating film-integrated ink ribbon which has an ink layer and an image-protective layer on the same surface thereof, includes a first step of applying the ink layer and the image-protective layer on the base film and rolling up the resultant laminate, followed by cutting the rolled laminate to form an elongated ribbon having a width corresponding to that of a final product, and a second step of rewinding the thus-formed ribbon around ribbon spools.
In the afore-mentioned first rolling step, the ink layer formed on a front surface of the base film is caused to come into contact with a back coat layer formed on a back surface of the base film, so that a considerable amount of dyes contained in the ink layer is transferred to the back coat layer. Further, in the second rewinding step, the rolled layer is unrolled and rewound around the ribbon spools while sequentially changing a roll diameter thereof. This procedure causes the change in contact position between the ink layer and the back coat layer, so that there arises a phenomenon that the dyes transferred to the back coat layer from the ink layer in the first step is re-transferred to the image-protective layer when rewound in the second step.
For this reason, when the laminating film-integrated ink ribbon produced according to the afore-mentioned process is used for image-printing, there is a likelihood that the dyes re-transferred to the image-protective layer is color-developed when laminated on the image and therefore unsuitable coloring is caused by the developed dyes on the image-protective layer. These problems become more remarkable in media having a higher sensitivity.
In order to eliminate these problems, it has been attempted to shorten the process time from the application of the ink layer up to the rewinding of the ribbon. This attempt has been found to be successful in reducing a risk of the re-transferring of the dyes to some extent, but associated with difficulties in process control, scheduling and the like. Alternatively, it has also been attempted to reduce the risk of the re-transferring of the dyes by using, as a composition of the back coat layer, those which are unlikely to cause the dye transfer. However, the back coat layer is required to exhibit lubricating properties and therefore any lubricant is to be added to the back coat layer, thereby increasing a tendency of the dye transferring.
Whereas, in the afore-mentioned conventional heat-transfer system, the image-protective layer has been uniformly transferred to the printing medium within the printer by means of a predetermined function thereof, so that the transferred image-protective layer has exhibited a uniform surface condition. In these conventional image formation techniques, it has not been considered that the image-transferred member is subjected to surface treatments generally used in silver salt photographs, such as semi-gloss finish treatments or silk finish treatments. For these reasons, the conventional heat-transfer system has not necessarily been suitable for general photograph applications to a sufficient extent.